Marin MBX 50 Feedback/Opinions? Weight

Want to go with aluminum for my 4 yr old son. Prices seem to range from $170 to $300+ for the BMW. Any take on the Marin would be appreciated. A little more than some, but has extra features too. Thanks for your time and opinions.

Of the three the MBX 50 is my favorite one to sell. As you noticed the Jet is a brick and handles like one too. The MBX is a pretty nice bike for a kid and also has the hand brake so he will learn to use it which will give you the chance to skip that interim smallish 20" and jump right to a geared bike for the next purchase.

Any update on this? My 4yo son is currently rocking a Scott Jr. Voltage 12 and is pretty much grown out of it. I like the look of this bike, but wanted to know if it is a tank like the little Scott, and if the suspension is actually appropriate for a 35-40 pound kid.

I'll give an update....I picked up one of these last week. It's a cool little bike. I haven't actually weighed it yet, but I'll do that today and post it. My son is about 35 lbs, and I think it will be fine for him. I paid $209, and of course the LBS gives free tune ups for life.
A couple comments...I had the bike shop trade out the training wheels for a kickstand, which they did for free, until I find a place to hang the biike. Doing the balance bike thing and didn't really want or need them.
Second, not sure what part of the country you are in, but Marin is out of these bikes, so the ones at dealers are the only ones out there. In FL, they are hard to come by. I called all the dealers on the west coast of FL, and only found one that had any bikes. Marin's next shipment will be of the blue 2010 models (per Marin), the red 2009 model is what's in stores. They were not sure if any bikes would be coming in before Christmas, so they advised not to depend on supply being available.
After the kids go to school, I'll weigh the bike (minus training wheels) and let you know.

I'm out here in Cali, and while a ways away, the San Francisco Marin factory store has them in stock, so that's good.

Can you please comment on 2 more aspects of the bike? Does the front suspension actually work/tuned for a little person? Is there a provision for a front brake on that fork (either a hole in the arch above the tire or canti brake boss holes)?

Ok, yep, bike has hole for a front brake. The shock is certainly functional and seems to work ok. I'm not really bike qualified enough to say if it is tuned to a 35 lb kid or not. You might check with others who post on this site as there are folks who sell these bikes and are much more familiar with them than myself. Or maybe even call Marin...I called them and a real person picked up right away and was very pleasant to speak with. Overall though, I find the quality high, the fit and finish well done, and the bright red color is something I think any little kid would find appealing.